Kamran BEHNIA
Heat travels in solids thanks to mobile electrons and phonons. Even in a detect-free solid, collisions degrade the flow due to the presence of the lattice. However, there are situations where most collisions for phonons, for electrons or for both conserve momentum. In this hydrodynamic regime, the quasi-particle viscosity plays a significant. Recent studies of thermal transport in a variety of solids such as strontium titanate [1], black phosphorus [2], graphite [3], and antimony [4] reveal a narrow temperature window where normal collisions enhance the heat flow rate. The ubiquitous T-square resistivity of Fermi liquids survives in dilute metals in absence of Umklapp events [5], indicating that it does not require momentum-relaxing collisions. Comparing the available transport data in metals and in normal liquid 3He indicates that energy diffusivity sets the amplitude of T-square thermal resistivitity, while momentum diffusivity (i.e. viscosity) is the driver of T-square electrical resistivitity [6].
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[3] Y. Machida et al., Science 367, 309 (2020)
[4] A. Jaoui, B. Fauqué, K. Behnia, Nat. Commun. 12, 195 (2021)
[5] J. Wang et al., Nat. Commun. 11, 3846 (2020)
[5] K. Behnia, Ann. Phys. 2100588 (2022).